FIG. 1 shows an exemplary network structure of a Universal Mobile Telecommunications System (UMTS). The UMTS system is generally comprised of a terminal (i.e., User Equipment (UE)), an UMTS radio connection network (UMTS Terrestrial Radio Access Network (UTRAN) and a Core Network (CN). The UTRAN includes one or more Radio Network Sub-systems (RNS), and each RNS is comprised of a Radio Network Controller (RNC) and one or more base stations (Node Bs) managed by the RNC. One eNode B may have one or more cells.
FIG. 2 shows an exemplary architecture of radio protocols used in the UMTS. The radio protocol layers exist as pairs between a terminal and the UTRAN and handle a data transmission over radio interface. Descriptions of each of the radio protocol layers will be given. First, the physical layer (Layer 1) serves to transmit data over the radio interface by using a variety of radio transmission technologies. The physical layer is connected to an upper layer called a medium access control (MAC) layer via a transport channel. The transport channel is divided into a dedicated transport channel and a common transport channel according to whether a channel is shared.
The second layer includes various layers, such as the MAC, RLC, PDCP and BMC layers. First, the medium access control (MAC) layer performs mapping various logical channels onto various transport channels, and performs logical channel multiplexing by mapping several logical channels onto a single transport channel. The MAC layer is connected with an upper layer called a radio link control (RLC) layer via a logical channel. The logical channel is divided into a control channel that transmits information of the control plane and a traffic channel that transmits information of the user plane according to a type of transmitted information. The MAC layer can be divided into a MAC-b sub-layer, a MAC-d sub-layer, a MAC-c/sh sub-layer, a MAC-hs sub-layer and a MAC-e sub-layer according to the type of transport channel being managed. The MAC-b sub-layer manages a Broadcast Channel (BCH), which is a transport channel handling the broadcasting of system information. The MAC-c/sh sub-layer manages a common transport channel, such as Forward Access Channel (FACH) or Downlink Shared Channel (DSCH), which is shared by a plurality of terminals. The MAC-d sub-layer manages a Dedicated Channel (DCH), which is a dedicated transport channel for a specific terminal. In addition, in order to support uplink/downlink high-speed data transmission, the MAC-hs sub-layer manages the High Speed-Downlink Shared Channel (HS-DSCH), which is a transport channel for high-speed downlink data transmission. The MAC-e sub-layer manages the Enhanced Dedicated Channel (E-DCH), which is a transport channel for high-speed uplink data transmission.
The Radio Resource Control (RLC) layer serves to guarantee various QoSs (Quality of services) required by each radio bearer (RB) and data transmission. Each RB has one or two independent RLC entities so as to guarantee RB-unique QoS, and the RLC layer provides three operational males: a TM (Transparent Male); a UM (Unacknowledged Male); and an AM (Acknowledged Mode) so as to support various QoSs. In addition, the RLC layer segments and/or concatenates data received from an upper layer to adjust the data size so as for a lower layer to suitably transmit the data to a radio interface.
The PDCP layer is located above the RLC layer. The PDCP layer performs a header compression function that reduces unnecessary control information such that data being transmitted by employing Internet Protocol (IP) packets, such as IPv4 or IPv6, can be efficiently sent over a radio interface that has a relatively small bandwidth. Thusly, the header compression increases transmission efficiency between radio interfaces by allowing the header part of the data to transmit only the essential information. Since the header compression function is basically provided in the PDCP layer, the PCDP layer exists only in a PS domain. A single PDCP entity would exist in each RB so as to provide the efficient header compression function to each of PS services.
The Broadcast/Multicast Control (BMC) layer of Layer 2 (L2) is located above the RLC layer. The BMC layer schedules a Cell Broadcast (CB) message, and broadcasts the CB message to terminals positioned in a specific cell or cells.
The Radio Resource Control (RRC) layer located at the lowermost portion of Layer 3 is only defined in the control plane. The RRC layer handles the control of parameters of the Layers 1 and 2 with respect to the setup (configuration), re-configuration and release of radio bearers (RB), and performs the control of logical channels, transport channels, and physical channels. Here, the RB refers to a logical path that is provided by the Layer 1 and Layer 2 of a radio protocol for data transfer between the mobile terminal and the UTRAN. In general, the setup of the RB refers to the process of stipulating the characteristics of a radio protocol layer and a channel required for providing a specific data service, and setting the respective detailed parameters and operation methods.
A Wideband Code Division Multiple Access (WCDMA) system has employed the High Speed Downlink Packet Access (HSDPA) and the High Speed Uplink Packet Access (HSUPA) technologies. In particular, these two technologies have been employed to effectively support the Packet Switched (PS) service. The HSDPA and the HSUPA may also be referred to as the HSPA.
The Circuit Switched (CS) scheme is a scheme for exchanging data by establishing a communication circuit between a transmitting side and a receiving side. In the CS scheme, a dedicated communication path is provided in advance between two stations desiring to communicate with each other, and the dedicated communication path is comprised of links for consecutively connecting each node. Each of the physical links is connected by a single channel, and thusly this would be appropriately and easily used in data exchange, which requires a relatively seamless flow, such as a telephone, a sensor, a telemetry input and the like. During data transmission, the CS scheme transmits data via the established communication circuit. Accordingly, it would be appropriate when transmitting a great amount of data or long messages, e.g., file transmission. A time division circuit switching employs a digital switching technology and multiplexing of a pulse code modulation in a digital communication circuit, thereby being greatly efficient for high-speed data transmission of a high quality. In this scheme, a dedicated (fixed) physical circuit between each of two end points is allocated, thereby minimizing a transfer delay from a time point at which data had been generated to a time point at which data transmission is started. In addition, since the dedicated (fixed) circuit is used, there is no transmission order reversal phenomenon in each data.
The Packet Switched (PS) scheme is a scheme that stores a data transmission unit having a certain length as a packet format in a transmitting-side packet switch. The PS scheme selects an appropriate communication path according to an address of a receiving side, and then transmits the same to a receiving-side packet switch. In the PS scheme, data is transmitted in data block units with a short length called a packet. In general, a length of the packet is limited to be approximately 1000 bytes. Each packet is comprised of a portion indicating user data and a portion indicating control information of a packet. Here, the control information of the packet should at least include information required to set a path of the packet within a network such that the packet is delivered to the receiving side. Once the packets are received by each node via the transmission path, the packets are first stored and then transmitted to the next node. Such storage process until the packet is delivered to the receiving side and the transmission process to the next node are repeated. In this scheme, a specific terminal does not continuously occupy a specific path, rather it occupies and uses the specific path only when needed, thereby maximizing efficiency of circuit usage. In addition, each data unit may be transmitted through different paths, thusly an amount of the transfer delay undergone by each data would differ.
Recently, mobile communication services have been developed to maximize efficiency in supporting a packet service, such as an Internet browsing and the like. Among those, a voice communication service is considered as the most important service in the mobile communications and is mainly provided through the circuit switched service.
Currently, the UMTS system has additionally employed R5 HSDPA and R6 HSUPA to support PS services, based on the R99 version WCDMA optimized for the CS service. That is, the current system supports both the CS network for the CS service and the PS network for the PS service. However, from the perspective of network operation, problems of a cost for installing the CS network and the PS network as well as of independently managing the two networks would occur.
To solve such problems, it would be expected to operate the PS network only, with gradual reduction in the support for the CS network. For this, there is a need to have a method for replacing all CS services with the PS services, or a method for effectively providing the CS services in the PS network.
In particular, there is a need to have a method for supporting the CS voice service representing the CS services in the PS network, i.e., in the HSPA network that employs the HSDPA and the HSUPA technologies.